The invention relates generally to modulation techniques in wireless communication systems.
Multiple-input multiple-output (MIMO) data transmission through sparsely-spaced antennas at both the transmitter and receiver provides a substantial increase in spectral efficiency of wireless links. MIMO transmission can potentially accomplish a multiplexing gain (i.e., an information rate increase due to virtual multiple wireless links) and a diversity gain (i.e., a spatial diversity due to multiple antennas in addition to time-domain and frequency-domain diversity). A key to realizing high data rates in such MIMO systems is a practical coded modulation scheme. From a data block size perspective, one may categorize prior art coded modulation schemes as follows. For small block size (e.g., smaller than ten), there are many solutions, such as orthogonal space-time block codes, linear dispersion codes, threaded algebraic space-time codes, and lattice space-time codes. When the block size is around several hundred, options include space-time trellis codes and “wrapped” space-time codes.
Consider, however, moderate-to-large block sizes (e.g., larger than a thousand) which are suitable for most data traffic in broadband communications. In this design regime, existing schemes are mostly based on powerful binary random codes (e.g., turbo codes or LDPC codes). They include bit-interleaved coded modulation (BICM), (see E. Zehavi, “8-PSK Trellis Codes for a Rayleigh Channel,” IEEE Trans. Communi., Vol. 40, pp. 873-84 (May 1992); Y. Liu et al., “Full Rate Space-Time Turbo Codes,” IEEE J. Select. Areas in Commun., Vol. 19, pp. 969-80 (2001)), multilevel coded modulation (MLC) (see H. Imai and S. Hirakawa, “A New Multilevel Coding Method using Error-Correcting Codes,” IEEE Trans. Inform. Theory, Vol. 23, pp. 371-77 (May 1977); L. J. Lampe et al., “Multilevel Coding for Multiple Antenna Transmission,” IEEE Trans. Wireless Commun., Vol. 3, pp. 203-08 (2004)), and stratified diagonal BLAST (see M. Sellathurai and G. Foschini, “Stratified Diagonal Layered Space-Time Architectures: Signal Processing and Information Theoretic Aspects,” IEEE Trans. Sig. Proc., Vol. 51, pp. 2943-54 (November 2003)). The recently proposed stratified D-BLAST is a coded D-BLAST, where different coding rates and transmission powers are assigned to different threads of D-BLAST. Among these schemes, BICM is considered to be simple and asymptotically capacity-approaching in both ergodic and non-ergodic channels, with the computation of a number of turbo receiver iterations. MLC requires channel-specific design of coding rates and constellation mapping functions for the different levels of MLC. On the other hand, MLC can be optimized for various objectives, such as providing unequal error protection. With the simple multi-stage decoding receiver, MLC is asymptotically capacity-approaching in ergodic MIMO fading channels—however is not so in non-ergodic fading channels.